1. Field of the Invention
The present invention relates to an electricity meter for measuring time integral of electric power consumption by a consumer's electric system.
2. Description of Related Art
Electricity meters for measuring time integral of electric power consumption of homes, offices and factories are widely used. An example of the electricity meter is disclosed in Japanese Unexamined Patent Application Publication No. 2004-226094 (page 10, FIG. 2). The disclosed electricity meter includes a detection unit, such as a current detector and a voltage detector, to detect electricity consumption of an objective system, a control unit to edit electricity consumption data from the detected electricity consumption, and a display unit to display the edited data.
According to the related art, the detection unit is not electrically insulated from the control unit and display unit. If a high voltage due to, for example, lightning is applied to the detection unit, the high voltage will be transferred from the detection unit to the control unit and display unit to damage them and destroy data accumulated in the control unit.